Research

21 pages, 3725 KiB

Open AccessArticle

On the Impact of Condensation and Liquid Water on the Radial Turbine of a Fuel Cell Turbocharger

by Tim Wittmann, Sebastian Lück, Christoph Bode and Jens Friedrichs

Machines 2022, 10(11), 1053; https://doi.org/10.3390/machines10111053 - 10 Nov 2022

Cited by 1 | Viewed by 2082

The air-management system of a proton exchange membrane fuel cell (PEMFC) is responsible for supplying the fuel cell stack with ambient air at appropriate conditions. The compressor of the air-management system can be partly driven by utilizing the fuel cell exhaust gas in [...] Read more.

The air-management system of a proton exchange membrane fuel cell (PEMFC) is responsible for supplying the fuel cell stack with ambient air at appropriate conditions. The compressor of the air-management system can be partly driven by utilizing the fuel cell exhaust gas in a turbine. The fuel cell exhaust is partially or fully saturated with water vapor. When the exhaust gas is expanded in the turbine, supersaturation occurs. This leads to the nucleation of droplets and their subsequent growth by condensation. This study provides an overview and understanding of the various phenomena caused by condensation and liquid water in the turbine of a PEMFC air-management system. The basis for this work is previously published numerical simulations that focused on individual aspects of the above phenomena. The present work revisits these results and puts them in context to provide a comprehensive understanding. Important phenomena are the effects of condensation on turbine performance through phase change losses, release of latent heat and thermal throttling. In addition, the released latent heat offers a power potential for downstream turbine stages. Through these effects, condensation can also impact the entire air-management system. However, condensation may occur unevenly, causing a circumferential asymmetry of the turbine outflow. Liquid water in the turbine can lead to droplet erosion, corrosion, and water-induced damage. In summary, it is essential to consider condensation and liquid water when developing turbines for PEMFC air-management systems. Full article

(This article belongs to the Special Issue High Speed Air Compressor for a Fuel Cell System for Use in a Vehicle)

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18 pages, 9308 KiB

Open AccessArticle

Design of a Herringbone-Grooved Bearing for Application in an Electrically Driven Air Compressor

by Henning Schlums, Christian Hühne and Michael Sinapius

Machines 2022, 10(8), 662; https://doi.org/10.3390/machines10080662 - 05 Aug 2022

Cited by 1 | Viewed by 1933

Abstract

A turbo compressor was investigated to ensure the operational reliability of the charging of fuel cell systems. This study investigated air-lubricated herringbone bearings to support the high-speed rotating shaft. For reliable operation of the rotor bearing system, stable operation in the whole speed [...] Read more.

A turbo compressor was investigated to ensure the operational reliability of the charging of fuel cell systems. This study investigated air-lubricated herringbone bearings to support the high-speed rotating shaft. For reliable operation of the rotor bearing system, stable operation in the whole speed range (up to 120 krpm), as well as low lift-off speed, is an important issue. Some publications containing guidelines for an optimized design in terms of stability and lift-off behavior date back to the 1970s, with some simplifying assumptions (such as narrow groove theory and small eccentricity analysis). Many publications have addressed the calculations, as well as the optimization of herringbone-grooved bearings; however, general design guidelines are still missing in the view of the authors. Although the investigations related to bearings for the support of a lightweight rotor for a special compressor of a fuel cell unit, this study could also indicate favorable bearing designs for other high-speed applications. Here, the compressible Reynolds equation was solved in the whole solution domain using a conservative finite difference scheme, and the corresponding bearing characteristics were determined. In a perturbation analysis, the linearized dynamic coefficients of the herringbone bearing are calculated. To compare the suitability and performance of the various herringbone-grooved bearing designs, especially at high speed, the simple model of a Jeffcott rotor airborne with two identical herringbone-grooved journal bearings (HGJBs) was used. The geometrical parameters of the HGJBs were varied, and their effects on bearing characteristics and stability were evaluated. Recommendations concerning favorable geometrical bearing parameters for a sufficiently high stability threshold speed and reasonable low lift-off speed were the result of the parameter study. Full article

(This article belongs to the Special Issue High Speed Air Compressor for a Fuel Cell System for Use in a Vehicle)

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18 pages, 2664 KiB

Open AccessArticle

Experimental Investigation of Two Switching States of an Active Foil Bearing during Start-Up

by Hannes Schmiedeke, Jan-Hinrich Sick and Michael Sinapius

Machines 2022, 10(6), 447; https://doi.org/10.3390/machines10060447 - 06 Jun 2022

Cited by 2 | Viewed by 2275

Abstract

The next few years will be marked by major changes in the mobility sector in order to come closer to CO

_{2}

neutrality. Especially in the commercial vehicle sector, fuel cells can make an important contribution. In order to achieve this, the efficiency [...] Read more.

The next few years will be marked by major changes in the mobility sector in order to come closer to CO

_{2}

neutrality. Especially in the commercial vehicle sector, fuel cells can make an important contribution. In order to achieve this, the efficiency of all subcomponents of a vehicle has to be improved. This also includes the bearings in the electrical air compressors. The frequent start–stop cycles are critical, as they can lead to higher wear and thus a shorter service life. One solution is a prototype that can actively switch between a triangular profile and a round bearing shape. In this work, the two switching states are investigated experimentally. Instead of the thin bearing sleeve of the prototype, rigid sleeves are used for each switching shape. This allows the shape itself to be studied without the contribution of the stiffness of the thin bearing sleeve along with the actuators. The examination includes static load tests and run-out tests in the range of the lift-off speed. Alongside this, the difficulties of the bearing production and the improvement of the test rig used are pointed out. Full article

(This article belongs to the Special Issue High Speed Air Compressor for a Fuel Cell System for Use in a Vehicle)

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17 pages, 2538 KiB

Open AccessArticle

Experimental Methods for Evaluating Components of Turbomachinery, for Use in Automotive Fuel Cell Applications

by Robin Vanhaelst, Dominik Begerow, Kay Bastian Timmann and Tim Kristian Liebe

Machines 2022, 10(3), 177; https://doi.org/10.3390/machines10030177 - 27 Feb 2022

Viewed by 1940

Abstract

This paper describes methods and test beds for components of turbomachinery, for use in automotive fuel cell applications at the Ostfalia University of applied sciences. Turbomachinery for use in fuel cell applications is subject to different requirements than those of conventional turbochargers. Therefore, [...] Read more.

This paper describes methods and test beds for components of turbomachinery, for use in automotive fuel cell applications at the Ostfalia University of applied sciences. Turbomachinery for use in fuel cell applications is subject to different requirements than those of conventional turbochargers. Therefore, the turbine and the air bearings of an electrical turbocharger will be subject to evaluation. The different boundary conditions in comparison to conventional turbochargers, with less heat and high humidity from the fuel cell, are especially of interest. Air bearings affect the friction and the vibrations/oscillations of the shaft. The methods and test beds need to fulfill the requirements of these types of turbomachinery. The friction test bed is modified with a new coupling solution, to ensure that the driving electric motor in combination with the shaft of the test component complies with the strict tolerances. For this, a magnetic coupling, for use in high-speed applications, is developed and tested on the friction test bed. The fuel cell turbine was adapted to the hot gas test bed and extended turbine maps are determined. To reach high humidity conditions of a fuel cell application, a water injection system is integrated into the test bed. Full article

(This article belongs to the Special Issue High Speed Air Compressor for a Fuel Cell System for Use in a Vehicle)

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21 pages, 1057 KiB

Open AccessArticle

Impact of Condensation on the System Performance of a Fuel Cell Turbocharger

by Sebastian Lück, Tim Wittmann, Jan Göing, Christoph Bode and Jens Friedrichs

Machines 2022, 10(1), 59; https://doi.org/10.3390/machines10010059 - 13 Jan 2022

Cited by 3 | Viewed by 2261

Abstract

A mobile fuel cell systems power output can be increased by pressure amplification using an electric turbocharger. These devices are subject to frequent transient manoeuvres due to a multitude of load changes during the mission in automotive applications. In this paper, the authors [...] Read more.

A mobile fuel cell systems power output can be increased by pressure amplification using an electric turbocharger. These devices are subject to frequent transient manoeuvres due to a multitude of load changes during the mission in automotive applications. In this paper, the authors describe a simulation approach for an electric turbocharger, considering the impact of moist air and condensation within the cathode gas supply system. Therefore, two simulation approaches are used: an iterative simulation method and one based on a set of ordinary differential equations. Additional information is included from turbine performance maps taking into account condensation using Euler–Lagrange CFD simulations, which are presented. The iterative calculation approach is well suited to show the impact of condensation and moist air on the steady state thermodynamic cycle and yields a significant shift of the steady state operating line towards the surge line. It is shown that a substantial risk of surge occurs during transient deceleration manoeuvres triggered by a load step. Full article

(This article belongs to the Special Issue High Speed Air Compressor for a Fuel Cell System for Use in a Vehicle)

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19 pages, 6549 KiB

Open AccessArticle

Analysing Efficiency and Reliability of High Speed Drive Inverters Using Wide Band Gap Power Devices

by Niklas Langmaack, Florian Lippold, Daiyi Hu and Regine Mallwitz

Machines 2021, 9(12), 350; https://doi.org/10.3390/machines9120350 - 09 Dec 2021

Cited by 6 | Viewed by 2590

Abstract

Within the project ‘ARIEL’ an electrical turbo compressor unit for fuel cell applications is deeply investigated. The necessary drive inverter is especially designed for high fundamental frequency and high switching frequency to cope with the requirements of the implemented electrical machine. This paper [...] Read more.

Within the project ‘ARIEL’ an electrical turbo compressor unit for fuel cell applications is deeply investigated. The necessary drive inverter is especially designed for high fundamental frequency and high switching frequency to cope with the requirements of the implemented electrical machine. This paper presents investigations on the inverter’s efficiency and its prospective lifetime at different stages of the development. In the design process different wide band gap power semiconductor devices in discrete packages are evaluated in terms of the achievable power density and efficiency, both by simulations and measurements. Finally, an optimised design using surface mount silicon carbide MOSFETs is developed. Compared to a former inverter design using silicon devices in a three-level topology, the power density of the inverter is significantly increased. The lifetime of power electronic systems is often limited by the lifetime of the power semiconductor devices. Based on loss calculations and the resulting temperature swing of the virtual junction the lifetime of the inverter is estimated for the most frequent operating points and for different mission profiles. Full article

(This article belongs to the Special Issue High Speed Air Compressor for a Fuel Cell System for Use in a Vehicle)

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17 pages, 3638 KiB

Open AccessEditor’s ChoiceArticle

Experimentally Validated Extension of the Operating Range of an Electrically Driven Turbocharger for Fuel Cell Applications

by Markus Schoedel, Marco Menze and Joerg R. Seume

Machines 2021, 9(12), 331; https://doi.org/10.3390/machines9120331 - 02 Dec 2021

Cited by 5 | Viewed by 2780

Abstract

From an aerodynamic point of view, the electric turbocharger for the air supply of an automotive fuel cell faces difficult requirements: it must not only control the pressure level of the fuel cell, but it also has to operate with very high efficiency [...] Read more.

From an aerodynamic point of view, the electric turbocharger for the air supply of an automotive fuel cell faces difficult requirements: it must not only control the pressure level of the fuel cell, but it also has to operate with very high efficiency over a wide range. This paper explores features for the compressor and the turbine of an existing electric turbocharger, which are intended to meet the specific requirements of a fuel cell in an experimentally validated numerical study. Adjustable diffuser or nozzle vanes in the compressor and turbine achieve wider operating ranges but compromise efficiency, especially because of the necessary gaps between vanes and end walls. For the turbine, there are additional efficiency losses since the pivoting of the nozzle vanes leads to incidence and thus to flow separation at the leading edge of the nozzle vanes and the rotor blades. An increase in the mass flow and a slight efficiency improvement of the turbine with the low solidity nozzle vanes counteracts these losses. For the compressor, a reduction in the diffuser height and its influence over the operating range and power consumption yields an increase in surge margin as well as in maximum efficiency. Full article

(This article belongs to the Special Issue High Speed Air Compressor for a Fuel Cell System for Use in a Vehicle)

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19 pages, 657 KiB

Open AccessArticle

Influence of Aerodynamic Preloads and Clearance on the Dynamic Performance and Stability Characteristic of the Bump-Type Foil Air Bearing

by Fabian Walter and Michael Sinapius

Machines 2021, 9(8), 178; https://doi.org/10.3390/machines9080178 - 23 Aug 2021

Cited by 3 | Viewed by 2388

Abstract

The dry lubricated bump-type foil air bearing enables a carrying load capacity due to a pressure build up in a convergent air film. Since the air bearing provides low power dissipation above the lift-off speed and the flexible foil provides an adaptivity against [...] Read more.

The dry lubricated bump-type foil air bearing enables a carrying load capacity due to a pressure build up in a convergent air film. Since the air bearing provides low power dissipation above the lift-off speed and the flexible foil provides an adaptivity against high temperatures, manufacturing errors or rotor growth, the bump-type foil air bearing is in particular suitable for high speed rotating machineries. The corresponding dynamic behavior depends on the operational parameters, the behavior of the flexible foil structure, and in particular on the circumferential clearance. In order to avoid or suppress the critical subsynchronous motion at high rotational speeds, many researchers recommend adding an aerodynamic preload to the bore shape, representing a transition from a circular to a lobed bearing bore shape. In addition to positive effects on the stability, preliminary studies demonstrated degrading effects on the stiffness and damping due to increasing preload values. This observation leads to the assumption, that the preload value meets an optimum with respect to stability, load-capacity, and lift-off speed. With the aim of deriving an appropriate lobe configuration for the design of the bump-type foil air bearing, this work performs comprehensive numerical investigations on the dynamic performance and the stability characteristic as a function of preload and minimum clearance. To this end, this work uses steady-state and transient stability analysis methods to recommend optimal aeroydnamic preload values with respect to the corresponding minimum clearance. Full article

(This article belongs to the Special Issue High Speed Air Compressor for a Fuel Cell System for Use in a Vehicle)

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